This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In studies performed during our previous proposals, we have been employing variable energy photoelectron spectroscopy in the valence and metal 2p regions to explore electronic relaxation, the change in electronic structure upon ionization of a reduced site. Thus far, this has been applied to Fe(SR)4 sites where the large electronic relaxation (ligand to M d CT) limits the charge change on oxidation and greatly reduces the geometry change (i.e. the reorganization energy of the site). We are now completing studies on a series of mononuclear Fe complexes in which we examined the effects of going from high to low spin and increased coordination number (tetrahedral vs. octahedral) as well as ligand variation to understand the contribution of heme ligation to electronic relaxation in the [Fetpp(imH)2] complex. We are now proposing to extend our PES studies of the bis-Im heme complex to the bis-met Fe(THT)2(tpp) complex and a cytochrome c model complex (Fe(C5-Im)(tpp)(THS).C6H6) where we will quantitate the effect of the met ligands on electronic relaxation and extend those results to electronic relaxation of cyt b vs. cyt c through DFT calculations and extended charge decomposition and valence bond configuration interaction analyses. In addition to PES studies of heme electron transfer sites, we will investigate covalency and electron delocalization and their contribution to electronic relaxation in blue copper, CuA, and Fe4S4 related model complexes.